The word itself has been widely recognized for a long time as "something you shout in the mountains". Even novels written in the 1950's have examples of ヤッホー.
In town, it may be used very occasionally as a humorous, unique greeting. Well, sometimes people feel おはよう is too uninteresting and want to say something different. I may have heard ヤッホー used ...
No one says yahoo in Japan.
Some decades (around 100-70) ago , Yahoo was used for making echo or voice call someone in the distance at mountain site. Yahoo is recognized as a calling in laud voice for distance , so It may use for joking. Never used as a popular greeting.
Decent people does not yahoo for greeting.